We started by prepping a piece of cardboard with a waxy rainbow and covering half of it with black.
This gave O some etching/scratching time while seeing the two effects; the black etchings stand out significantly better with such a strong contrast in the background.

Then we got to work on a transfer sheet.
If I had read Tiny Rotten Peanuts post in depth, I would have made the rainbow stripes closer together.
We folded the sheet in half and O used the edge of a fork to make her mark, before opening a surprise piece of work.